In a medium bowl, combine tuna, scallion, cilantro, ginger, garlic-chili sauce, ponzu, sesame oil, and soy sauce. Chill 20 minutes.
To serve, place in 6 chilled martini glasses. Garnish each serving with cilantro and place 2 rice crackers into the tuna at an angle. Or scoop 1 tablespoon mixture onto each of 12 spoons and arrange in a circle (handles pointing out) on a serving plate; garnish with cilantro.
Cold-Storage Tip Chopping fresh tuna finely by hand will be easier if you pop it in the freezer for about 20 minutes beforehand.